How Do Formal Charge and Resonance Relate in Molecular Structures?

[kougou]

Hi

Just wondering, what is the relationship between formal charge and resonance?

formal charge is used to determine which lewis structure is most plausible.
Resonance is hybri between two "correct" lewis structure having different electrons distribution but the element position must stay stationary.

Say NOCl. We could have two different formal charges of NOCl. Does it mean it also has a resonance strcuture?

 

[Yenaled]

Formal charge is used to determine which structure has the lowest energy (greatest stability).

Take NOCl. O=N-Cl has formal charges of 0 on all the atoms. The structure O-N=Cl has formal charges of -1 on O and +1 on Cl. Such a structure would be super unstable (very high energy) that it won't exist. After all, it's much easier to form O=N-Cl, why would we ever want O-N=Cl?

Resonance occurs when we have two structures of similar energy, resulting in electron delocalization.

I hope that answers your question.